Stands for Personal Zoot.
Zoot is another term for a cannabis cigarette in London cannabis culture. A P.Z. (Personal Zoot) is a joint that one has rolled and will only be smoked by that person. This usually occurs when there is a large group with a large amount of cannabis to be smoked in one session, in celebration of a cause/subject or when someone is smoking on their own.
Dave: I'm hella bored. What shall we do tonight?
Rooster: Lets roll a couple of P.Z.'s and smoke like kings man!